PeterHermesFurian/iStock/Thinkstock(RAQQA, Syria) -- Four hundred U.S. Marines will be leaving Syria soon after completing their mission to help defeat ISIS in Raqqa, the city the terror group once claimed as its capital in Syria, coalition officials said Thursday.

"With the city liberated and ISIS on the run, the unit has been ordered home," the Combined Joint Task Force for Operation Inherent Resolve said in a statement. "Its replacements have been called off."

The U.S.-led coalition fighting ISIS announced that troops from an artillery unit with the 1st Battalion, 10th Marine Regiment will soon leave Syria after providing crucial artillery support to the Syrian Democratic Forces (SDF), the Kurdish and Arab rebel group fighting ISIS in Syria.

The SDF retook the city of Raqqa from ISIS in mid-October after an intense, street-to-street fight involving an estimated 2,500 ISIS fighters.

An earlier Marine artillery unit had arrived in May in advance of the offensive to retake Raqqa, according to officials, and they provided artillery fire for the SDF forces that retook the Taqba Dam from ISIS before moving on to Raqqa.

"With a 155-mm artillery battery in the fight, their mission was to deny and disrupt ISIS from gaining ground or moving from their defensive positions," said Marine Artillery Lt. Col. Jon O'Gorman, chief of forces for Operation Inherent Resolve. "These Marines rained relentless and highly accurate firepower on the enemy."

According to military officials, there are approximately 2,000 U.S. military service members in Syria, although the official Defense Department force level is set at 503 personnel. A Defense Manpower Data Center quarterly personnel report listed about 1,700 American troops in Syria as of September 30, but Pentagon officials have described that report as a "snapshot" of force levels that are constantly varying.

"The departure of these outstanding Marines is a sign of real progress in the region," said Inherent Resolve's director of operations, Brig. Gen. Jonathan Braga. "We're drawing down combat forces where it makes sense, but still continuing our efforts to help Syrian and Iraqi partners maintain security."

"Our remaining forces will continue to work by, with, and through partner forces to defeat remaining ISIS [fighters], prevent a re-emergence of ISIS, and set conditions for international governments and NGOs to help local citizens recover from the horrors of ISIS's short-lived rule," Braqa added.